<!DOCTYPE html>
<meta charset="utf-8">
<style>
body, html {
    margin: 0;
}
#a {
    position: absolute;
    top: 0;
    left: 0;
    height: 200px;
    width: 600px;
    background: gold;
}
#b {
    position: absolute;
    top: 100px;
    left: 0px;
}
</style>
<div id=a></div><div id=b>X

